Why do guys like to share share there girlfriends its not anything I would ever do is this something a girl does to please her man or does she enjoy having sex with another guy while he watches?
Big-haired Bitch/Personality Hire
As far as the first half of your question, you should ask the guys.
Now as for the part in which you addressed us ladies, I'd say that some of us do it for various reasons. Some of us do it because we find it exciting, and if it turns on our man, it's an added bonus. Perhaps some women can be forced into it, but that's rare. So no, it's not something done strictly to please our men. It's for mutual pleasure.
░P░U░S░S░Y░ ░I░N░ ░B░I░O░